1. Field of Invention
The present invention relates to a method for reducing or completely stopping the water inflows in the case of an underground formation containing hydrocarbons into a borehole which has been drilled there. Using this method, it is possible to shut out water without thereby reducing the passage of oil and/or of hydrocarbon gas into the borehole.
2. Description of the Prior Art
Water often exists as a saline solution in the same formation as oil or gas. The extraction of oil or of hydrocarbon gas is thus accompanied by the extraction of water in such an amount as to give rise to considerable problems; directly or indirectly it causes the precipitation of salts in the vicinity of the borehole or in the borehole itself, it considerably increases the corrosion of all metal parts underground or above ground, it increases, without any benefit, the quantities of the liquids pumped, transferred and stored, and it produces emulsions with the oil which are difficult to break above ground and which, below ground, form blockages in the cavities of the formation.
According to the prior art, numerous methods have been proposed and practiced whose purpose is to reduce the water inflows into the boreholes for the extraction of oil or hydrocarbon gas. The methods frequently consist in the introduction of an impregnable barrier in the formation between the water and the borehole or between the water and the oil or hydrocarbon gas. The agents commonly introduced block almost as much oil or hydrocarbon gas as water. The components of this barrier may be: cement, resins, suspensions of solid particles, paraffins or water-soluble polymers which are crosslinked in the deposit by means of the introduction of so-called cross-linkers.
At present polymers are used, the polymers introduced as a solution into the porous environment, adsorbed on the surface of the solid and project into the space of the pores so as to be suitable for reducing into the water inflows by friction. In contrast, the non-aqueous fluids such as oil or especially hydrocarbon gas pass the adsorbed macromolecules which now take up a negligible volume on the wall and thus leave the passage completely free.
U.S. Pat. No. 4,095,651 discloses the use of hydrolyzed polyacrylamides. It has been found, however, that this polymer type is effective mainly with respect to water having a low salt content and is degraded by water having a higher salt content. At elevated temperatures said polymers, in the presence of polyvalent ions, tend to form precipitates which may block the pores of the rock formations.
U.S. Pat. No. 4,718,491 discloses the use of polysaccharides. While these compounds, which are difficult to inject into the pore space, have the effect of retarding or reducing the influx of water, they permit only incomplete working of the existing deposits and/or lose their effect at higher temperatures.
U.S. Pat. No. 4,842,071 discloses the use of non-hydrolyzed acrylamide polymers or copolymers which are hydrolyzed by the subsequent introduction of an aqueous basic solution. This method has drawbacks in terms of additional effort required due to the introduction of a further solution and due to the problem of reaching the injected polymer solution with the basic solution which is applied subsequently, and with regard to increased corrosion susceptibility of the equipment used. Furthermore, the polymer solution is effective only upon reaction having taken place with the aqueous basic solution, the efficiency being determined by the extent of the reaction.